Immunogenicity of lipid nanoparticles and its impact on the efficacy of mRNA vaccines and therapeutics

Abstract

Several studies have utilized a lipid nanoparticle delivery system to enhance the effectiveness of mRNA therapeutics and vaccines. However, these nanoparticles are recognized as foreign materials by the body and stimulate innate immunity, which in turn impacts adaptive immunity. Therefore, it is crucial to understand the specific type of innate immune response triggered by lipid nanoparticles. This article provides an overview of the immunological response in the body, explores how lipid nanoparticles activate the innate immune system, and examines the adverse effects and immunogenicity-related development pathways associated with these nanoparticles. Finally, we highlight and explore strategies for regulating the immunogenicity of lipid nanoparticles.

Fig. 1. TLR and RLR signaling pathways and the effects of LNPs.

A TLRs include TLRs 3, 7, 8, and 9 on the endosome surface as well as the rest of the TLRs on the cell membrane surface. When a TLR recognizes a foreign antigen, downstream signals are activated, starting with the MyD88 adapter, except for TLR3. Transcription factors such as AP-1, NF-kB, CREB, c/EBP, and IRF3 ultimately migrate to the nucleus and initiate the innate immune response. When transcription factors are activated, cytokines, chemokines, and type 1 IFNs are activated, and innate immunity occurs. RNA is recognized by endosome TLRs 3, 7, 8, and 9, and LNPs encapsulated with mRNA can be recognized by the MyD88 adapter. B When foreign RNA is recognized by MDA5 and RIG-1, RNA helicases in the cytosol and by STING proteins on the surface of the endoplasmic reticulum, the RLR signaling pathway is activated. It activates the transcription factors NK-κB and IRF3 through MAVS, a signaling adapter protein, and promotes cytokines and type 1 IFNs. At this time, LNP can activate MDA5 to trigger immunity.

Fig. 2. NLR and IFN-mediated signaling pathways and the effects of LNPs.

A NLRs recognize external substances or stress and induces NLRP3 to generate a nuclear signal complex called the inflammasome to initiate an inflammatory response. Caspase-1 converts pro IL-1 and IL-18 into IL-1 and IL-18, respectively. Caspase-1 products such as IL-1β later promote MyD88-dependent signaling. When IL-6R is activated, STAT3 and NF-κB are activated by downstream signals to secrete cytokines and chemokines. LNP can be recognized by the NLRP3 inflammasome, IL-6 receptor, and MyD88 to initiate immune action. B Viral antigens can trigger type 1 interferon. IFNα and IFNβ produced by the innate immune process act on IFNAR1 and IFNAR2 to activate ISG transcription through the ISG promoter. IFNα/β causes cells to enter an antiviral state by expressing ISG. Downstream of IFNAR, various pathways, such as mTOR, JAK-STAT, and MAPK, are activated to express chemokines, cytokines, and antiviral effectors. However, PKR induces phosphorylation of eIF2α, which reduces eIF2 activity and prevents mRNA translation.

Fig. 3. Adverse effects of LNPs.

A Mechanisms of vaccine adverse responses, including IgE-mediated allergy, IgM-mediated pseudoallergy, and autoimmune reactions. PEGylated LNPs lead the body to generate anti-PEG antibodies, which can have negative side effects. IgE antibodies bind to FcεRI in mast cells or basophilic granulocytes, key cells of the immediate hypersensitivity reaction. Multiple tyrosine kinases are activated as mediators. B Upon administration of the PEGylated liposome, anti-PEG IgM in the body binds to the liposome, and this complex causes complement activation via the classical complement pathway and is quickly removed from the blood circulation due to Kupffer cell phagocytosis, which is called the accelerated blood clearance (ABC) phenomenon. This anaphylatoxin induces inflammatory mediators by stimulating macrophages, mast cells and basophils. This mediator binds to receptors of autonomic effector cells, endothelial cells, and smooth muscle cells and induces CARPA through activation. C mRNA-LNP-based drugs can cause autoimmunity as follows: (1) mRNA plays the role of autoantigen and triggers the autoimmune process through TLR7; (2) Since LNPs themselves act as an adjuvant, the autoimmune process proceeds through the innate immune response to LNPs; and (3) in the case of mRNA-LNP vaccines, the autoimmune response can be further aggravated because the vaccine itself enhances the immune process.

Fig. 4. How to modulate the immunogenicity of LNPs.

Even a slight modifications can change the properties of an LNP. A Altering the molar ratio of PEG or adjusting the formulation rate changes the size of the LNP in the formulation. B The charge of the LNP is modified by replacing or adding phospholipids to a charged lipid. C Moreover, there are techniques for altering PEG lipids. D To improve the efficacy of mRNA-LNP vaccines, adjuvants are being introduced. Adjuvants can be used to enhance the effectiveness of further immunizations. E There are several methods for administering mRNA-LNP vaccines, including intravenous (IV), intramuscular (IM), intradermal (ID), subcutaneous (SC), and intranasal (IN). An appropriate route of administration must be determined based on an understanding of the anatomy of the inoculation site and the induced immune action.